Passing $\mathrm{H}_2 \mathrm{~S}$ gas into a mixture of $\mathrm{Mn}^{2+}, \mathrm{Ni}^{2+},…
Passing $\mathrm{H}_2 \mathrm{~S}$ gas into a mixture of $\mathrm{Mn}^{2+}, \mathrm{Ni}^{2+}, \mathrm{Cu}^{2+}$ and $\mathrm{Hg}^{2+}$ ions in an acidified aqueous solution precipitates
$\mathrm{CuS}$ and $\mathrm{HgS}$
$\mathrm{MnS}$ and $\mathrm{CuS}$
$\mathrm{MnS}$ and $\mathrm{NiS}$
$\mathrm{NiS}$ and $\mathrm{HgS}$
Solution
In acidic medium, $\mathrm{H}_2 \mathrm{~S}$ is very feebly ionized giving very small concentration of sulphide ion for precipitation. Therefore, the most insoluble salts $\mathrm{CuS}$ and $\mathrm{HgS}$ are precipitated only.